This invention relates to an aluminum-based metal link including a shaft portion and a bushing mount portion connected with an end portion of the shaft portion, for example, an aluminum-based metal link useable as a suspension link of vehicles.
Friction Stir Welding (FSW) is known as one of connection techniques for joining two members made of aluminum-based metal, together. The FSW is accomplished by rotating a friction stir welding tool while contacting with a joint or junction of the two members. The two members are heated at the joint by friction contact with the rotating friction stir welding tool so that base materials of the two members are plasticized and stirred to form a weld joint at which the two members are welded together. The FSW can join the two members at a relatively low temperature as compared with a temperature at which other related techniques such as metal electrode inert gas (MIG) welding are conducted. Therefore, upon producing an aluminum-based metal link having a shaft portion and a bushing mount portion joined to an end portion of the shaft portion, if the bushing mount portion is connected with the end portion of the shaft portion using the FSW, the connection can be sufficiently accomplished without giving adverse influence on nearby components because of the low temperature of the FSW. For instance, a rubber bushing directly attached to the bushing mount portion by vulcanizing adhesion can be prevented from suffering from undesired thermal influences such as reduction of adherence strength, at the FSW process.
FIG. 5 illustrates an aluminum-based metal link having bushing mount portion 2 connected with shaft portion 1 by the FSW. As illustrated in FIG. 5, shaft portion 1 is formed into a hollow cylindrical shape. Bushing mount portion 2 has a small-diameter end portion. First, bushing mount portion 2 is abutted on an end portion of shaft portion 1 by inserting the small-diameter end portion into the end portion of shaft portion 1. In this butt joint state, the outer circumferential surfaces of the end portion of shaft portion 1 and the small-diameter end portion of bushing mount portion 2 are flush with each other. FIG. 6 shows friction stir welding (FSW) tool 5 for the FSW. Friction stir welding tool 5 has base portion 7 and a cylindrical rod 9 connected with base portion 7. FSW tool 5 is rotated and brought into contact with the outer circumferential surfaces of the end portions of shaft portion 1 and bushing mount portion 2 which extend near along the butt joint portion or junction. In this condition, friction heating is produced, which plasticizes the base metal of respective shaft portion 1 and bushing mount portion 2. FSW tool 5 is moved along the line of the junction which extends over the outer circumferences of the end portions of shaft portion 1 and bushing mount portion 2, while being kept rotated in contact with the outer circumferential surfaces along the junction line. The base metal of respective shaft portion 1 and bushing mount portion 2 are plasticized and stirred, so that the end portions of shaft portion 1 and bushing mount portion 2 are welded together to form the link. When the welding is completed, FSW tool 5 is retreated from weld joint portion W of the link. Weld joint portion W of the link is thus formed with hole 3 through which FSW tool 5 is removed from weld joint portion W.
Generally, a bending moment is applied to a suspension link of vehicles as well as large compressive and tensile forces are repeatedly exerted thereon. The bending moment acts on rubber bushing 4 mounted to bushing mount portion 2. Here, if rigidity, namely, resistance against deformation, of rubber bushing 4 is measured with respect to torsional force Rx acting about axis O1 of rubber bushing 4 and torsional force Rz acting about axis O2 that intersects axis O1 and axis X of shaft portion 1, the rigidity of rubber bushing 4 against torsional force Rz is lower than that against torsional force Rx, and therefore rubber bushing 4 is readily deformable in the direction of torsional force Rz. The bending moment acts on rubber bushing 4 in the direction of axis O1.
Assuming that bending moment is applied to the link with hole 3 which is located such that a center axis thereof is parallel to axis O1 of rubber bushing 4, the maximum stress based on the bending moment will be caused at hole 3 so that hole 3 is deformed. This will lead to reduction of mechanical strength of the link. Accordingly, after the FSW is finished, it will be required to do additional work for filling hole 3 by a suitable method such as metal electrode inert gas (MIG) welding. This will lead to increase in the production cost of the link.
It is an object of the present invention to provide an aluminum-based metal link capable of increasing the strength and reducing the production cost.
According to one aspect of the present invention, there is provided an aluminum-based metal link comprising:
a shaft portion extending along a first axis, said shaft portion having opposed axial end portions;
at least one bushing mount portion having a second axis perpendicular to the first axis; and
at least one weld joint portion in which one of the opposed axial end portions of the shaft portion and the bushing mount portion are welded together by friction stir welding (FSW), the weld joint portion extending along outer peripheries of the one of the opposed axial end portions of the shaft portion and the bushing mount portion and formed with a hole having a third axis angularly offset from the second axis about the first axis, the hole being formed upon termination of the FSW.
According to a further aspect of the present invention, there is provided a method for producing an aluminum-based metal link comprising a shaft portion that extends along a first axis and has opposed axial end portions, at least one bushing mount portion that has a second axis perpendicular to the first axis and comprises a small-diameter portion and a large-diameter portion having a same outer diameter as the shaft portion, and at least one weld joint portion in which the bushing mount portion is welded to one of the axial end portions of the shaft portion, the weld joint portion being formed with a hole having a third axis angularly offset from the second axis about the first axis, the method comprising:
forming the shaft portion and the bushing mount portion from workpieces, respectively;
press-fitting the small-diameter portion of the bushing mount portion into the one axial end portion of the shaft portion until an end face of the large-diameter portion of the bushing mount portion is abutted on an end face of the one axial end portion of the shaft portion to form a junction of the large-diameter portion of the bushing mount portion and the one axial end portion of the shaft portion;
relatively rotating the shaft portion with the bushing mount portion and a friction stir welding (FSW) tool and, at the same time, rotating the FSW tool while keeping the FSW tool in contact with the junction, to thereby form the weld joint portion along the junction;
terminating the relative rotation of the FSW tool and the shaft portion with the bushing mount portion when the FSW tool reaches a terminal position in which the FSW tool is angularly offset from the second axis about the first axis; and
removing the FSW tool from the weld joint portion at the terminal position to thereby form the hole in the weld joint portion and thus provide the link having the hole formed in the weld joint portion.